In accordance with increasingly strict exhaust gas regulations for gasoline engines and compression ignited internal combustion engines, the start of injection, for example, for compression ignited engines, may be adjusted to the particular operating phase of the engine. In the cold start phase, for example, at low outside temperatures, the start of injection of diesel distributor injection pumps must be advanced, thus making a low-emission start with reduced particle emission and reduced noise possible. As the rotational speed of the compression ignited engine increases, the delivery start of the injection pump may be advanced in order to compensate for the time shift caused by the delayed injection and ignition.
After the injection operation, diesel fuel may require a certain time period to form an ignitable mixture, which self-ignites at high pressure. The time period required for this purpose between injection start and combustion start is known in compression ignited internal combustion engines as ignition delay. The ignition delay is determined, among other factors, by the ignitability of the diesel fuel (expressed by the cetane number), the achievable compression ratio of the compression ignited internal combustion engine, and the quality of fuel atomization by the injection nozzle of the fuel injector. The ignition delay of compression ignited engines may be on the order of magnitude of 1-2 ms. During the cold start phase, for example, at low outside temperatures, this time period becomes longer, resulting in soot production by the uncombusted fuel, which is discharged into the environment through the exhaust system.
In the case of distributor injection pumps of compression ignited engines, different cold start accelerators may be used. A hydraulic measure for accelerating cold starts is to temporarily raise the internal pressure of the distributor injection pump during the cold start and during the immediately subsequent cold running phase of compression ignited internal combustion engines. As the internal pressure is raised, an injection timing piston is displaced, resulting in the injection start being advanced. The disadvantage of this measure is the subsequent loose run of the injection timing piston due to the slow decrease in pressure in the interior of the distributor injection pump.
Another option for advancing the injection start is to advance the injection timing piston and thus the injection start by rotating a component designed as a roller ring during the start and during the cold running phase of the compression ignited engine. Another measure which may be carried out using mechanical means is to displace the injection timing piston by pressing on one side of the injection timing piston using a cam shaft so that the injection start is advanced. Using the above-mentioned measure, a small amount of adjustment may be possible, limited by the mechanical overstress of the components involved, and thus only a limited advance of the injection start may be achievable.
The displacement of the injection timing piston in the direction of advancing the injection start takes place during the cold phase by opening the inlet bore using a trailing piston. The trailing piston may also be designed, for example, as a servo piston or a regulating slide. The function of this component is to open and close the inlet and the outlet of the injection timing piston.
In the cold position of the distributor injection pump, the pressure chamber associated with the timing piston is initially empty; it begins to fill up during the subsequent warm-up phase of the engine as the rotational speed increases. As the interior of the distributor injection pump gradually fills up, the internal pressure increases.
The injection timing piston is adjustable with a short response time using a cold start accelerator piston. At the low rotational speeds that occur in the start phase of the engine, an earlier loose run of the injection timing piston may be achieved without the need for a complete high-pressure buildup in the interior of the pump. A high-pressure buildup in the pump chamber is not required for the method according to the present invention; therefore, the injection timing piston may be advanced in a timely manner so that an earlier injection may be achieved even during the first revolutions of the engine. An earlier injection may improve fuel atomization during injection, so that the ignitability of the fuel mixture within the combustion chamber increases. According to the present invention, this may result in both reduced particle emission during the start and cold running phase and in quicker starting of the compression ignited engine.
The injection timing piston of the distributor injection pump may be advanced for an earlier injection start using a trailing piston, which opens or closes an inlet bore. The trailing piston, which may be moved by a spring-sleeve combination, may be supported by a cold start accelerator piston whose front extends into a pressure chamber. The trailing piston, which may be designed, for example, as a regulating slide various embodiment options, opens and closes the inlet and outlet of the injection timing piston, so that the latter shifts the injection timing according to the operating state of the compression ignited engine. When the distributor injection pump and the engine are cold, the engine has no pressure in this pressure chamber, so that the front of the cold start accelerator piston protrudes into this pressure chamber. The end of the cold start accelerator piston facing away from the front face functions as a movable support surface for the spring-sleeve combination of the trailing piston. The cold start accelerator piston is in turn displaced by the pressure in the pressure chamber of the cold start accelerator unit. At start and during the cold running phase of the engine, the pressure chamber is empty and is not filled until the start of the warm-up phase of the engine. This increases the pressure in the pressure chamber, the cold start accelerator piston is displaced so that the trailing piston assumes its normal position, and the injection start advance is reversed.
In addition, it is possible to operate external triggering devices, such as a load-dependent delivery start timer, for example, using the cold start accelerator piston of the distributor injection pump. This function is activated via an annular groove, for example. When the compression ignited engine is cold, this external triggering device is off, i.e., the orifice designed as a groove, for example, or the corresponding bore remains closed. As the compression ignited engine gradually warms up, the load-dependent delivery start timing function may be turned on, because the internal pressure in the interior of the distributor injection pump increases. The load-dependent delivery start timing is triggered when the orifice is open.